Method and apparatus for pneumatically separating solid particles



April 1968 w. WOCHNOWSKI ETAL 3,

METHOD AND APPARATUS FOR PNEUMATICALLY SEPARATING SOLID PARTICLESOriginal Filed March 27, 1952 V 5 Sheets-Sheet l INVENTORS 4 [Jamar Muwe April 16, 1968 w WOCHNOWSKI ETAL 3,378,140

METHOD AND APPARATUS FOR PNEUMATICALLY SEPARATING SOLID PARTI CLESOriginal Filed March 27, 1952 5 Sheets-Sheet 2 INVENTOR5 A, 2: (Z44144w: (wwa p 1968 w. WOCHNOWSKI ETAL. 3,378,140

METHOD AND APPARATUS FOR PNEUMATICALLY SEPARATING sous PARTICLESOriginal Filed March 27, 1952 5 Sheets-Sheet 5 mom United States Patent3,378,140 METHOD AND APPARATUS FOR PNEUMATI- CALLY SEPARATING SOLIDPARTICLES Waldemar Wochnowski, Hamburg, Heinz Harte, Hamburg-Bergedorf,and Johannes Iwen, Reinbek, near Hamburg, Germany, assignors to HanniWerke, Koerber & Co., KG, H'amburg-llergedorf, Germany Originalapplication Mar. 27, 1962, Ser. No. 182,802, now Patent No. 3,265,209,dated Aug. 9, 1966. Divided and this application Aug. 9, 1966, Ser. No.571,236 Claims priority, application Germany, Oct. 31, 1960, H 40,822;Mar. 27, 1961, H 42,131 9 Claims. (Cl. 209-137) ABSTRACT OF THEDISCLOSURE A separator for pneumatically separating solid particles in ahousing having an inlet at its bottom through which a gaseous suspensionof solids is projected along an incline-d path, a plurality of bafl lesdefining inclined passages through which portions containing lightparticles of the suspension are diverted and evacuated from the top ofthe housing. The heavy particles, which drop out of the suspension in anarea of the housing below the ats sages, are evacuated at the bottom ofthe housing.

This application is a division of our application Ser. No. 182,802,filed Mar. 27, 1962, now US. Patent 3,265,209 issued Aug. 9, 1966.

The present invention relates to a method and ap paratus for separatinglighter particles from heavier particles, particularly for separatinglighter tobacco articles from a mixture of lighter and heavier tobaccoparticles.

An important object of our invention is to provide a method ofcontinuously separating lighter particles from heavier particles whichform a mixture with the lighter particles so that the heavier and/ orlighter particles may be continuously conveyed to a further processingstation and that the separation of lighter particles from heavierparticles is completed within short periods of time.

Another object of the invention is to provide a method of the justoutlined characteristics which is especially suited for separatingtobacco ribs from tobacco leaf laminae and which may be carried out atsuch a speed that the consistency of processed material remainsunchanged or changes very little during the separating operation.

A ttuther object of the invention is to provide a method which may becarried out in a fully automatic way and which may be resorted to forseparation of large quantities of tobacco leaf laminae from tobacco ribsso as to satisfy requirements for mass-manufacture of tobaccocontainingproducts.

An additional object of the invention is to provide an apparatus whichmay be utilized to carry out the above outlined method and which isconstructed and assembled in such a way that it may be rapidly andconveniently converted for use with different types of mixturesincluding lighter and/or heavier particles of different specific weight,moisture content, configuration, thickness, flexibility or othercharacteristics, and which requires little attention once it is adjustedand started to carry out the method.

Still another object of the invention is to provide an apparatus of thejust outlined characteristics for sep arating ribs from tobacco leaflaminae: with the help of one or more air currents which is constructedand assembled in such a way that the laminae are separated from the ribswithin very short periods of time and that the consistency, particularlythe moisture content, of the laminae is not appreciably affected duringshort-lasting contact with air.

A concomitant object of the invention is to provide an apparatus forseparating tobacco ribs from tobacco leaf laminae by subjecting amixture of ribs and laminae to the action of one or more air currentswhich is constructed in such a way that the mixture is subdivided intolighter and heavier fractions in one or more stages to make sure thatany heavier particles which might have been entrained by the bulk of thelighter particles are also separated from the lighter particles, or viceversa.

An additional object of the invention is to provide an improved assemblyfor separating the mixture of tobacco leaf laminae and ribs immediatelyafter and at the same rate at which the mixture is being formed in astemming or destalking machine.

Briefly stated, one feature of the present invention resides in theprovision of a method of separating lighter particles from a mixture oflighter and heavier particles. The method comprises the steps ofintroducing into the lower part of an inclined ascending path an aircurrent containing a mixture of lighter and heavier particles andconveying the air current at such a speed that the current entrains themixture into an intermediate part of the inclined path, subdividing theair current leaving the intermediate part of such path into a pluralityof partial currents and conveying the partial currents through separateportions or passages of the upper part of the inclined path at such aspeed that the partial currents entrain only lighter particles wherebythe heavier particles descend by gravity and leave the inclined path,separating the lighter particles from the partial air currents, andcollecting the heavier particles.

The passages in the upper part of the inclined path are preferablyconfigurated in such a way that the partial currents are accelerated ontheir way to the separating zone.

In accordance with another feature of the present invention, thedescending heavier particles are preferably conveyed through a secondcurrent of air which travels counter-current to heavier particles atsuch a speed that it entrains at least some lighter particles whichmight have been entrained with the heavier particles. This secondcurrent is preferably merged with at least one of the partial currentsso that all of the lighter particles can be separated from air in acommon separating zone.

The lower and intermediate parts of the inclined path preferably divergeupwardly so that the first air current expands and its speed decreasessufiicicntly to allow for gravitational descent of heavier particles.The second air current is preferably conveyed in a second upwardlydiverging path so that its velocity also decreases to allow forsubstantially unimpeded descent of heavier particles.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved apparatus itself, however, both as to its construction and itsntode of operation, together with additional features and advantagesthereof, will be best understood upon perusal of the fo'lowing detaileddescription of certain specific embodiments with reference to theaccompanying drawings, in which:

FIG. 1 is a somewhat schematic perspective view of an apparatus whichembodies one form of our invention;

FIG. 2 is a partly elevational and partly vertical sectional view of aseparator assembly which forms part of the apparatus shown in FIG. 1;

FQG. 3 illustrates a vector diagram indicating the mannor in whichgravity and o;her forces act upon lighter particles in the separatorassembly of BIG. 2;

FIG. 3a illustrates a vector diagram indicating the action of variousforces upon the heavier particles which enter the separator assembly ofFIG. 2; and

FIG. 4 is a partly elevational and partly vertical sectional view of amodified apparatus.

Referring first to FIG. 1, there is shown a separating apparatus whichcomprises a housing 2 resembiing an up right tower and forming part of aseparator assembly (to be described in greater detail in connection withFIG. 2), a stemming or destalking machine 202 whose hopper 203 isprovided with an outlet 204 through which a mixture of tobacco leaflaminae (lighter particles) and ribs (heavier particles) produced by themachine 262 is adrnilted into a first current of air flowing through asupply duct 9. Unstemmed tobacco leaves are delivered by a conveyor 212which discharges into a chute 201 provided on the machine 202. Anevacuating duct 18 conveys air and lighter tobacco particles into an airextractor 267 provided wih an air lock 268 adapted to discharge a streamof lighter particles onto the upper stringer of a take-off conveyor 299.

The apparatus of FIG. 1 also comprises a source of compressed air, hereshown as a blower 266, whose outlet is connected to a pressure conduit205 connecting to the supply duct 9. The inlet of the blower 296 isconnected with a suction conduit 210 which draws air from the evacuatingduct 18. A branch conduit 211 connects the outlet of the blower 206 witha secondary separator chamher in the housing 2.

FIG. 2 illustrates all details of the separator assembly which isaccommodated in the housing 2. The upper pOrtion of this housingaccommodates a series of specially configurated baffles which definethree passages 53, 54, 55 constituting the upper part of an ascendinginclined path whose intermediate part is constituted by a primaryseparator chamber 1. The intake ends 50, 51. 52 of the passages 53, 54,55 receive lighter tobacco particles which are entrained by an ascendingair current admitted through the supply duct 9. The lower portions 56,57, 58 of the walls 59, 60, 61 (respectively bounding the left-handsides of the passages 53, 54, 55) are inclined with reference to avertical plane. The lower portions 57, 58 of the walls 60, 6.1 areformed with wedge-shaped guide surfaces 64, 65 for lighter particleswhich ascend with three partial air currents toward a duct and/or intothe evacuating duct 18. The right-hand sides of the passages 53, 54 arerespectively bounded by walls 62, 63. The discharge ends 66, 67, 68 ofthe passages 53, 54, and the discharge end of the evacuating duct 15communicate with the evacuating duct 13. The wall 59 makes an acuteangle with an outer wall 29, and the wall 69 bounding the righthand sideof the duct 53 makes an acute angle with the left-hand wall of themedian passage 54. Furthermore, the right-hand wall 7t? of the medianpassage 54 makes an acute angle with the left-hand wall 61 of the thirdpassage 55. The other wall 71 of the passage 55 makes an acute anglewith the lower wall 72 of the duct 15.

A valve 73 is articulately connected to the upper end portion of thewall 71 by a hinge 74 so that it may regulate the cross-scctional areaof the duct 15. A similar valve 75 is secured to the upper end portionsof the walls 61, by a hinge 76, and a thi d hinge '78 connects a valve77 to the upper end portions of the walls 60, 69. The valves 73, 75, 77are adjustab e by means of suitable linkages 24% one of which is shownin FIG. 1. The uppermost valve 73 extends deeper into the evacuatingduct 13 than the valves 75, 77 and is function is to change the amountsof air which are drawn through the passages 53-55. The distribution ofthe partial air currents flowing through the passages 53, 54, 55 may beregulated by appropriate adjustment of the valves and 77. The valves 73,75 and 77 enable the operators to adjust the apparatus for separation ofdifferent types of mixtures.

The operation of the separator assembly shown in FIG. 2 is as follows:

The mixture of lighter and heavier tobacco particles is admitted intothe ascending inclined air current which enters the lower part 1a of theaforementioned path through the supply duct 9. The heavier particles arepermitted to descend by gravi y as indicated by the arrow 80 and enterthe lower part of a secondary separator chamber 10. The velocity ofpartial air currents fiowihg through the passages 53, 54, 55 is selectedin such a way that they entrain a substantial percentage of lightertobacco particles and advance the lighter particles directly into theevacuating duct 18. The lighter particles in the remainder of theascending air current pass along a wa'l 13 and are lifted into theintake end of the duct 15 to advance toward and into the evacuating duct18. The second air current which is admitted into the secondaryseparator chamber 10 via branch conduit 211 flows countercurrent toheavier particles and merges with the first air current. This secondcurrent lifts such lighter particles which might have been entrained bythe descending heavier particles. The heavier particles are evacuatedthrough an air lock 5 driven by a motor 6 and the lighter particles arewithdrawn from the evacuating duct 18 todescend onto the conveyor 209shown in FIG. 1. Any heavier particles which might have been lifted tothe level of the intake ends 50, 51, 52 of the respective passages 53,54, 55 are slowed down near the walls which define these passages anddescend into the secondary separator chamber 10.

The vector diagram of FIG. 3 illustrates the manner in which the aircurrents in the separator chambers 1 and 10 of the assembly shown inFIG. 2 act upon the lighter tobacco particles. The force represented bythe vector b is the force with which the partial currents urge thelighter particles into the passages 53, 54, 55. The vector g representsthe force of gravity, the vector a represents the force acting upon themixture of lighter and heavier particles by the current of air which isadmitted through the supply duct 9, the vector 0 indicates the resultantof forces represented by the vectors a and g, and the vector 2represents the resultant of forces indicated by the vectors b and c. Theresultant vector e makes a small acute angle with the vector a andpoints into the passages 5355. The vector c points into the upper partof the secondary separator chamber 10. The inclination of the vector ais the same as that of the wall portions 57, 58, 59.

The diagram of FIG. 3a shows the manner in which the air currents in theseparator chambers 1 and 10 and other forces act upon the heaviertobacco particles. The force represented by the vector g is the force ofgravity, and the vector a indicates the force produced by the aircurrent admitted through the supply duct 9. The vector c' is theresultant of the forces represented by vectors g and a, and this vectorpoints toward the lower part of the secondary separator chamber 10. Thevector b indicates the force acting upon heavier particles in thechamber 1 in a direction of the passages 5355, and the vector f is theresultant of forces represented by the vectors b, c. This vector f alsopoints toward the lower part of the secondary separator chamber 10.

FIG. 4 illustrates a second apparatus for separating lighter tobaccoparticles from heavier particles. This apparatus comprises a destalkingassembly 301 including a destalking machine 301' mounted on a frame 301aand receiving unstemmed tobacco leaves from a non-illustrated conveyorwhich discharges into a chute 319. The mixture 347 of lighter andheavier tobacco particles produced by the machine 301' is dischargedinto a hopper 302 whose outlet 303 admits the mixture into a supply duct304 connected to a separator assembly 305. The intake end of the supplyduct 304 is connected to a pressure conduit 310 which is connected tothe outlet of a source of compressed air here shown as a blower 309. Theintake of the blower 309 in connected with a suction conduit 308 whichis further connected to an air extractor 307. The latter communicateswith the upper end of the separator assembly 305 through an evacuatingduct 306. The duct 306 delivers lighter tobacco particles to the airextractor 307 which discharges lighter particles through an air lock 317and onto the upper stringer of a take-off conveyor 318.

The blower 309 discharges surplus air through a nozzle 311 which iscontrolled by a valve 312, the latter having a manually actuatedhandgrip portion 312a. At the junction of the pressure conduit 310 andsupply duct 304, there is provided a regulating device in the form of arotary valve 313 which may be turned by means of a handle 313a tothereby adjust the strength of the current of compressed air whichpasses from the outlet of the blower 309 and through the supply duct 304to entrain a stream of the mixture 347 into the separator assembly 305.

At the upstream side of the regulating valve 313, the pressure conduit310 communicates with the intake end of a pressure pipe 314 whichconveys a second current of compressed air to a pair of upwardlyextending branch pipes 315, 316 connected to the separator assembly 305.

The separator assembly 305 comprises a housing 321 which resembles anupright tower. This housing is mounted on a frame 320 and includes anupwardly divering inclined funnel-shaped mixture-receiving channel ordiffusor 322 bounded at its underside by a convex lower wall 325 and atits upper side by a convex upper wall 324. The channel 322 constitutesthe lower part of an inclined ascending path whose intermediate part isconstituted by a primary separator chamber 323. The upper zone of thespace in the housing 321 accommodates three profiled baffles 329, 330,331. These bafiles define between themselves a pair of arcuate passages327, 328 communicating with the evacuating duct 306. The baflle 329 andthe wall 324 define between themselves a third passage 326, and a fourthpassage 346 is provided between the baflie 331 and the top Wall 3210 ofthe housing 321. The passages 326 and 346 communicate with theevacuating duct 306 and constitute the upper part of the aforementionedpath. At the upper ends of the baffles 329-331, there are providedvalves 332, 333, 334 fixed to horizontal shafts 332a, 333a, 334a whichcan be rotated by suitable handles (not shown) located externally of thehousing 321.

The shafts 332a-334a enable the operator to adjust the respective valves332-334 and to thereupon maintain the valves in selected positions inorder to determine the rate of air flow through the passages 326320 and346.

The blower 309, pressure conduit 310, supply duct 304 and pressure pipe314 together constitute a pneumatic conveyor whose function is toadvance the mixture 347 into the primary separator chamber 323 and toconvey blasts of compressed air into a secondary separator chamher 335.

The upper region of the primary separator chamber 323 communicates withthe upper region 336 of the secondary separator chamber 335, and thisupper region 336 is in communication with the passage 346. The lowerregion of the secondary separator chamber 335 is bounded by afunnel-shaped upwardly diverging wall 337 which includes two mutuallyinclined perforated or apertured sections or screens 330, 339. Thesescreens converge toward an air lock 340 which serves as a means forevacuating heavier particles from the secondary chamber 335. The screen333 separates the chamber 335 from a plenum chamber 342 whichcommunicates with the branch pipe 315 and is further bounded by thelower wall 325 of the channel 322, by the bottom wall 341 of the housing321, and by the front and rear end walls 321a, 321b of the housing. Thewalls 321a, 321b also bound the separator chambers 323, 335 and theevacuating duct 306. The front Wall 321a is broken away in FIG. 4 toexpose the interior of the separator assembly 305.

The right-hand end wall 343 of the housing 321, the screen 339, thewalls 321a, 321b, and the bottom wall 341 define between themselves asecond plenum. chamber 344 which communicates with the branch pipe 316.The flow of air through the branch pipes 316, 315 is respectivelyregulated by valves 348, 349 which may be adjusted by hand. The air lock340 discharges heavier tobacco particles onto the upper stringer of asecond takeoff conveyor 345- which is mounted below the bottom wall 341and is provided with inclined side walls 345a, 34 5b forming a troughand serving as a means for guiding the heavier particles onto the upperstringer of this conveyor.

The apparatus of FIG. 4 operates as follows:

Unstemmed tobacco leaves are admitted through the cliute319 and enterthe destalking machine 301 wherein the heavier particles (mainly ribs R)are separated from lighter tobacco particles (mainly tobacco leaflaminae L). The resulting mixture 347 is discharged into the hopper 302to form a continuous stream which passes through the outlet 303 into thesupply duct 304. The current of air passing through the supply duct 304entrains the mixture into and through the channel 322. While advancingthrough the supply duct 304 and channel 322, certain heavier componentsof this mixture (almost exclusively ribs R) descend toward and advancealong the lower wall 325 to be discharged into the secondary separatorchamber 335. This is due to the fact that the ribs are heavier than theleaf laminae. Of course, some ribs might remain entangled between thelighter particles as the mixture passes through the supply duct 304 andthrough the channel 322; such ribs are then advanced into the primaryseparator chamber 323. The right-hand end portion of the lower wall 325is nearly horizontal to otter little resistance to forward movement ofheavier particles into the secondary separator chamber 335. Such heavierparticles drop onto the screen 338 and advance toward the air lock 340to be evacuated onto the take-off conveyor 345. Any lighter particleswhich might have been entrained by the heavier particles are separatedtherefrom by jets Y of air passing from the plenum chamber 342 throughthe apertures in the screen 338 so that such lighter particles rise inthe secondary separator chamber 335 and enter the upper region 336 to bedrawn into the passage 346 and thence into the evacuating duct 306.Thus, a preliminary separation of heavier tobacco particles from lighterparticles takes place right in the lower part (channel 322.) of theaforementioned inclined path, and such separation is thereupon continuedin the primary separator chamber 323. The inertia of heavier tobaccoparticles which have entered the chamber 323 (mainly ribs R which remainin the partially sorted mixture) causes such heavier particles toadvance into the secondary separator chamber 335 Where they drop bygravity and slide along the screens 338, 339 toward and into the airlock 340 to be evacuated onto the conveyor 345. Any heavier particleswhich are entrained by the lighter particles toward the passages 326,327, 328 and 346 are slowed down near the inclined surfaces of thebaffles 329, 330, 331 and by the top wall 3210 of the housing 321 sothat such heavier particles begin to move countercurreut to the flow ofair and descend into the lower region of the secondary separator chamber335. The lighter particles L advance with the partial air currentsflowing through the passages 326-323 and 346 and accumulate in the airextractor 307. It was observed that the major percentage of heavierparticles is separated from lighter particles while the mixture moveswith the ascending inclined air current advancing toward and into thepassages 326-328 and 346 so that the secondary separator chamber 335 ismainly a settling compartment for the heavier particles R. In FIG. 4,the current of 'air discharged by the pneumatic conveyor and theportions of this current travelling through the passages 3264628 and 346are identified by reference characters X. The jets Y of air admittedfrom the plenum chambers 342, 344 through the screens 338, 339 form asecond current YY which ascends through the secondary separator chamber335 countercurrent to descending heavier particles and thereupon mergeswith the currents X to form therewith a single current Z advancing intothe evacuation duct 396 and air extractor 397. Any lighter particles Lwhich might have entered the secondary separator chamber 335 are liftedby the current X flowing into the passage 346 and by the second currentYY so that the particles descending by gravity onto the wall 337 consistexclusively or nearly entirely of ribs R. The separating action in thesecondary chamber 335 is surprisingly effective and this is attributedto the fact that the volume of this chamber is comparatively large andalso because the chamber 335 receives a smaller percentage of theoriginal mixture 347. Therefore, the material which enters the upwardlydiverging chamber 335 is free to expand so that the lighter particlesare fully exposed and may be subjected, individually, to the liftingaction of the air current YY. Hardly any leaf laminae will descend intothe air lock 340.

The lighter particles which accumulate in the air extractor 307 areseparated from the air current which latter is evacuated through thesuction conduit 308, and the condensed stream of lighter particles isthen evacuated through the air lock 317 to descend onto the conveyor318. This conveyor advances the lighter particles to a furtherprocessing station, not shown. The air which is withdrawn by the blower309 through the suction conduit 308 is thereupon recirculated throughthe pressure conduit 310 and enters the supply duct 304 as well as thepipe 314 to bring about separation of a next batch of the mixture 347.

It is to be understood that, while we have described the operation ofthe separating apparatus in connection with segregation of tobacco leaflaminae from tobacco ribs, this apparatus is equally useful fortreatment of other types of material wherein a heavier solid fraction isadmixed to a lighter solid fraction.

The current X is strong enough to move the lighter particles L throughthe lower part 322 of the inclined path and into the upper regions ofthe chambers 323, 335 but is weak enough to permit gravitational descentof heavier particles R into the lower region of the secondary separatorchamber 335. On the other hand, the current YY is just strong enough tocounteract the gravity of lighter particles L which might have enteredthe lower region of the secondary separator chamber 335 and to entrainsuch lighter particles into the passage 346. The descent of heavierparticles R is affected by the second current YY very little or not atall.

The passages 3263 28 and 346 converge toward the evacuating duct 306 toaccelerate the lighter particles therein. The channel 322 and chamber323 diverge upwardly so that the speed of the air current admitted bythe supply conduit 304 decreases sufficiently to allow for gravitationaldescent of the heavier particles which leave the inclined path and enterthe secondary separator chamber 335.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featureswhich fairly constitute essential characteristics of the generic andspe- 8 cific aspects of our contribution to the art and, therefore, suchadaptations should and are intended to be comprehended within themeaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is:

l. Apparatus for separating lighter particles from a mixture of lighterand heavier particles, comprising a housing defining an ascending pathhaving lower intermediate and upper parts; a plurality of baillesprovided in said housing to divide said upper part into a plurality ofseparate passages which are inclined with respect to and communicatewith said intermediate part to divert a portion of the lighter particlesin said mixture, one of said baflies defining with a portion of saidhousing an additional passage for the remainder of the lighter particlesin said mixture; means for admitting into the lower part of said path anair current containing said mixture of lighter and heavier particles atsuch a speed that the mixture ascends into said intermediate part butthat the heavier particles descend in said intermediate part by gravitywhile the lighter particles continue to rise with partial air currentswhich result from subdivision of said air current on entry into saidpassages, said intermediate part including a separator chamber whereinthe heavier particles are separated from the lighter particles wherebythe lighter particles travel with said partial air currents in saidpassages; evacuating means for withdrawing said partial currents and thelighter particles from all of said passages; and means for evacuatingheavier particles from said separator chamber.

2. Apparatus as set forth in claim 1, wherein said separator chamberdiverges upwardly to effect gradual reduction in the speed of said aircurrent.

3. Apparatus as set forth in claim 2, wherein said housing furtherincludes a secondary separator chamber p0- sitioned to receive heavierparticles which leave said first mentioned chamber and in communicationwith at least one of said separate passages, and further comprisingmeans for admitting into said secondary chamber a second ascendingcurrent of air at such a speed that the second current entrains into theupper part of said path at least some lighter particles which might havebeen entrained by the heavier particles.

4. Apparatus as set forth in claim 3, wherein said housing comprisesapertured wall means bounding the lower part of said secondary chamberand said second air current is admitted through such apertured wallmeans.

5. A method of separating lighter particles from a mixture of lighterand heavier particles, comprising the steps of introducing into thelower part of an inclined ascending path an air current containing amixture of lighter and heavier particles and conveying the air currentat such a speed that the current entrains the mixture into anintermediate part of said path; decelerating the air current in saidintermediate part to effect gravitational descent of heavier particlesso that the thus decelerated current is at least substantially free ofheavier particles; subdividing the de'celerated air current and thelighter particles remaining therein into a plurality of partial currentsby conveying the air of said decelerated current through separateportions of the upper part of said p'ath at a speed which suffices toentrain the lighter particles; separating the lighter particles from thepartial air currents; and evacuating the heavier particles from theintermediate part of said path.

6. A method as set forth in claim 5, further comprising the step ofaccelerating the partial currents in the upper part of said p'ath.

7. A method as set forth in claim 6, further comprising the step ofmerging said second current with at least one of said partial currents.

8. A method as set forth in claim 7, wherein the lower and intermediateparts of said inclined path diverge upwardly so that the first mentionedcur-rent exp-ands and is decelerated sufiiciently to allow forgravitational descent of heavier particles, said second current beingconveyed in a second upwardly diverging path so -that its velocitydecreases sufficiently to allow for substantially unimpeded descent ofheavier particles.

9. A method as set forth in claim 5, further comprising the step ofconveying said descending heavier particles through a second current ofair which travels counter-current to heavier particles at such a speedthat it entrains at least some lighter particles which might have beenentrained by the heavier particles.

References Cited UNITED STATES PATENTS 1,143,587 6/1915 Marsden 209-139X 4,877,861 9/1932 Hatch 2()9137 X 2,728,632 12/1955 Ma'theson 209157 X3,010,576 1 1/1961 Harte 209-133 FOREIGN PATENTS 40,716 5/ 1937Netherlands.

FRANK W. LU'ITER, Primary Examiner.

